A known filter element includes a pleated filter media formed into a hollow cylinder. The longitudinal seam of the pleated cylinder is normally secured with adhesive or by a metal clip. In a common configuration, a plurality of longitudinally extending pleats project radially from a central axis.
Annular end caps are attached on both ends of the cylinder, encapsulating the pleats. One end cap has a central aperture providing fluid communication with the interior of the filter element and an inside-out flow pattern. The other end cap is closed and prevents access to the interior of the element. U.S. Pat. Nos. 5,250,179 and 7,090,772 disclose pleated bag filters of this general type.
The filter element is fitted inside a support basket of the same cylindrical shape. The support basket is manufactured of a material having a plurality of openings to permit flow. Common support basket materials are perforated hard plastic or steel, or wire mesh. The closed end cap fits inside the basket and typically faces the floor of the support basket. To encapsulate the outer tips of the pleated media, the closed end cap is larger in diameter than the pleated cylinder.
Held in place by the end cap, when pressurized, the media stretches outwardly toward the inner wall of the support basket. In operation, stress may accumulate in the filter media at the point where the pleats attach to the closed end cap, and tears can occur in the filter media proximate to this junction.
Support scrim or netting may be co-pleated on the outside of the filter media to retain the pleats. However, this raises manufacturing and selling costs. Unsupported filter media is much more economical. When pressurized, however, unsupported filter media tends to advance into and lodge in the openings of the support basket. A filter element that is dry and clean upon insertion is wet and dirty and in intimate contact with the support basket at change-out. The filter element often becomes stuck and difficult to extract.
Common solutions include various extraction tools. In practice, if the filter element can be slightly dislodged that is usually sufficient to offset the impinged media from the openings in the support basket allowing removal to proceed. But these extraction tools involve an additional operational step, and extra expense. Devices and provisions in the support basket itself to “pop-up” the filter element from the bottom are also seen. They, too, involve additional hardware and operational steps.
Another approach involves modifying the shape of the support basket and filter element from a true cylinder to a cone shape. U.S. Pat. No. 5,916,435 discloses cone-shaped support basket configured to receive a cone-shaped filter element. Although this approach reportedly facilitates ease of change-out, it limits filter element selection to those custom-coned for a particular basket shape. Yet another approach involves the introduction of a flexible support ring (U.S. Pat. No. 5,736,040) or internal spring (U.S. Pat. No. 7,469,906) into the end cap. Both of these techniques require additional components and manufacturing steps.